离散题目14

#include<stdio.h>int main(){int n, m;while(scanf("%d %d", &n, &m) != EOF){int a[1005][1005];int x, y;while(m--){scanf("%d %d", &x, &y);a[x][y] = 1;}int flag = 1;int i, j;for(i = 1; i <= n; i++)for(j = 1; j <= n; j++){if(a[i][j] != a[j][i])flag = 0;}if(flag)printf("YES\n");elseprintf("NO\n");}return 0;}